1. Field of the Invention
The present invention relates to a semiconductor device and an information processing system including the semiconductor device, and particularly to a semiconductor device that can dynamically changes an operating frequency and an operating voltage, and an information processing system including the semiconductor device.
2. Description of Related Art
In recent years, a DVFS (Dynamic Voltage Frequency Scaling) function has been often used in logic-based semiconductor devices such as system LSIs (Large-Scale Integration) used for mobile devices and the like and MPUs (Micro-Processing Unit) used for personal computers and server computers so as to achieve a high performance and a low power consumption. The semiconductor devices equipped with the DVFS function can dynamically change an operating frequency and operating voltage of circuit blocks included therein depending on processing power requirements of the circuit blocks (See Japanese Patent Application Laid-Open No. 2011-81800). If the logic-based semiconductor devices are equipped with the DVFS function, it is possible to obtain a high performance during a high load operation, as well as to dramatically reduce current consumption during a low load operation.
However, in semiconductor memory devices such as DRAM (Dynamic Random Access Memory), part of a memory cell array may perform an analog operation that is not in synchronization with a clock signal. Therefore, if the semiconductor memory devices employ the DVFS function, the memory cell array may not work properly. As one example, in the case of DRAM, if the DVFS function is used to change a selection voltage of a word line or an array voltage that is written into a cell capacitor, the problem arises that an operating margin of the memory cell array significantly decreases.